Community: The study group members reminisce about their favorite times together as the school year winds down in this new episode (8 p.m. NBC).

American Idol: This results episode features performances by David Cook and Katy Perry. (8 p.m. Fox).

Royal Wedding of a Lifetime: This new series draws parallels between Catherine Elizabeth Middleton and Princess Diana (8 p.m. Lifetime). New episodes follow at 9 and 10.

The Paul Reiser Show: Paul (Paul Reiser) is asked to pick up Jonathan's (Ben Shenkman) son for a play date when Claire (Amy Landecker) is delayed at the dentist. Henry Rollins guest stars in this new episode (8:30 p.m. NBC).

True Hollywood Story: Sarah Palin is featured in this new episode (10 p.m. E!).

24 Hour Restaurant Battle: Exes Laura and Eric reunite to face off against another former couple in the premiere of this new cooking series (10 p.m. Food).

Randy Jackson Presents: America's Best Dance Crew: The Black Eyed Peas assign their songs to the crews in this new episode (10 p.m. MTV).

SPECIALS

The 12,000-Bottle Boat: This new special follows a six-person catamaran made entirely from plastic beverage bottles as it sets out on a 1,500 voyage and makes an ecological statement (5 and 8 p.m. National Geographic).